The present invention relates to a molding glass lens and a mold thereof, especially to a mold that includes at least three protrudent parts with the same height disposed in the form of a circle on an outer circular part of a cavity of molding units for achieving better air-exhaust efficiency. Moreover, the molding glass lens formed includes grooves on outer corresponding to the protrudent parts on mold.
The glass precision molding technology has been applied to manufacture spherical and aspherical glass lens with high resolution, good stability and low cost such as lens disclosed in US2006/0107695, US2007/0043463, TW095101830, JP63-295448, and TW095133807. By feature of melting at high temperature, a glass preform is set between upper and lower mold units then processes in vacuum, heated and pressured. Where, the glass preform can be a ball, a gob, a plate, a disc, or polished semi-finished blank. Thus the optical surfaces of upper and lower molding units have been transferred to the soft preform. After cooling, a molding glass lens with optical surfaces is released from the molds.
Since the preform contacts closely with the upper and the lower molds during processes being heated and pressured, once there is a little residual air between preform and molding units, a bubble is formed on optical surface of the lens and this leads to poor quality of the lens. Because the glass preform is set on the lower molding unit, air inside the cavity of the lower molding unit can't be exhausted completely due to pressure from gravity of the glass preform against the lower mold unit when the mold is vacuumed. The following approaches are disclosed in prior arts for solving problems of residual air:
Refer to JP2002-003225, JP05-286730, JP06-191861, US 20050172671, and EP0648712 etc, the problems of residual air is solved by pressure control, temperature control or surface roughness. However, when material, shape or size of the glass preform is changed, the operation conditions should also be changed. Thus control of only single parameter can't solve the problem.
Refer to JP61-291424, TWI248919, JP2000-044260, TW200640807, US20050242454, air channels are disposed on the mold so that air can escape during processes of being heated and pressured. However, such design only works for the glass preform with ball or gob shape. The plate or disc-shaped preform may block the air channels during heating process so that the air exhaust efficiency is reduced.
Refer to JP61-291424, JP08-337428, and U.S. Pat. No. 7,159,420, a groove or an air vent is disposed on the molding unit, especially the lower molding unit. But by such design, corresponding protrudent may occur on the molded lens and this lead to problems in following processing or assembling. In order to reduce size of the protrudent, the size of the groove is restricted and this cause low air-exhaust capability.
Generally, air exhaust effect is represented by air-exhaust efficiency δ that equals to the cross-sectional area of air-exhaust channels divided by volume of the mold cavity (δ=cross-sectional area of air-exhaust channels/volume of the mold cavity). The larger the air-exhaust efficiency δ is, the less air accumulates during the molding process. On the contrary, if the air-exhaust efficiency δ is getting smaller, it's difficult to exhaust the air. The results of long-term experiments show that δ value of the plate or disc-shaped glass preform should be larger than, said 1.0. Review to the prior arts with disposition of air channels on the mold, once the cross-sectional area of air-exhaust channel is large enough, δ is nearly 0.25 only. Yet a lot of melt glass will overflow into the air-exhaust channel to form the brim. A further processing is required to shape the brim. Moreover, prior arts with a plurality grooves on the lower molding unit, several protrudents generate on the molding glass lens. Since the protrudents on the surface of lens, the assembling difficulty is leaded. For reducing the protrudents of lens, the cross-sectional of the groove should be smaller, but the air bubble problems propagates due to air-exhaust efficiency is getting poorer by low δ value.
Therefore, while molding glass lens made by precision glass-molding technology, the design of the mold requires higher air-exhaust efficiency δ. And the molding glass lens should not include any protrudent or brim that requires shaped processing or affects assembling of the lens. Thus both requirements of mass production and high yield rate can be satisfied.